It is conventional practice to manufacture high pressure hydraulic hose or the like by first extruding a hollow tube of elastomeric material, and then drawing the extruded tube upon a cylindrical supporting mandrel. The supported tube is then spirally wrapped with a number of fabric reinforcing tapes, and then with additional tapes of elastomeric material for forming the outer hose cover. Where the hose is designed for very high pressure or vacuum applications, it is also common to helically wind one or more reinforcing wires between the layers of the reinforcing tapes. The entire assembly is then placed in an elongate steam vulcanizing chamber, wherein the extruded tube and wrapped tapes are cured and adhered together to form an integral hose. As a final step, the mandrel is withdrawn, typically by using hydrostatic pressure to axially push the mandrel from the hose.
Hose manufactured by the above conventional procedure necessarily has a relatively thick inner core layer, since the extruded tube which forms this layer must be sufficiently thick to provide adequate strength to permit the tube to be drawn over the supporting mandrel. Thus the inner core layer imparts unnecessary rigidity to the hose, and it contains more material than would otherwise be required.
Difficulties have also been encountered in maintaining the quality of hose produced by the above conventional procedure. In particular, it is common for air to be entrapped between the various tape layers during the manufacturing process, resulting in air pockets being formed in the wall of the hose. As will be apparent, these air pockets significantly reduce the structural integrity of the wall, and can result in the premature failure of the hose. Further, it is difficult to achieve a uniformity in the thickness of the layers, and to achieve a smooth internal bore, in hose produced by the above conventional process.
It is also known to extrude the tube directly onto a moving mandrel by a procedure known as "cross heading" in the industry. While this procedure eliminates the step of drawing an extruded tube upon a mandrel, it nevertheless requires the shaping and handling of a relatively thin and hot plastic material, and undesirable deformation or the formation of pin holes in the material are very real problems.
It is accordingly an object of the present invention to provide a method and apparatus for fabricating hose which effectively overcomes the above deficiencies in known manufacturing processes.
It is a more particular object of the present invention to provide a method and apparatus for producing a high quality, relatively lightweight and flexible elastomeric hose, and which permits the hose to be fabricated in a variety of constructions which are specifically designed for the transmission of solid, liquid, gaseous, or other fluid material, and under low, medium, or high pressure or vacuum conditions.
It is another specific object of the present invention to provide a method and apparatus for producing a hose of the described type and which is characterized by a relatively thin and flexible inner core layer which has a smooth bore, by uniform reinforcing and cover layers, and by the substantial absence of air pockets or pin holes in the wall thereof.
It is a further object of the present invention to provide a highly efficient and economical method and apparatus for the continuous fabrication of high pressure hose in extremely long lengths, and wherein the need for a vulcanizing chamber is eliminated.